I’m so sorry OP you’re going through this.
Whenever you start to doubt yourself about their relationship just think to yourself ‘would he be doing this with a male friend?’ e.g my own DP wouldn’t be up late at night texting a lad most evenings and chatting on the phone and making him a makeshift desk and going for meals etc. individually he may do it as in, go for a meal and catch up with one of his mates. But he wouldn’t also be let night texting that same friend regularly if you get me.
I don’t know any platonic friendships between a man and woman that are this intense. Because they’re not. Not unless:
- they are related.
- one is going through a short term crisis e.g cancer diagnosis, house fire etc.
- They are in the beginning stages of dating.
He may not have left you for her, because she doesn’t want him too? Most men don’t leave a stable relationship and home without another woman waiting with open arms. Id she’s encouraging him to work on your relationship then she may not want him like that, or she could be aware that if she encourages him then she’s committed herself to an entanglement/love triangle. She may like him, but not enough for her to enter into such a situation.
Either way, you shouldn’t be in this situation to begin with.
On a slightly different note, you say your relationship is good/functional but not romantically passionate. Can this be sustained from his side long term? This female friend may brush him off, but the next woman may not. If he is aware of the lack of sexual spark between you both, and craves it, then sooner or later he will find it. You can’t spend your life looking over your shoulder.